The present invention relates to a new and improved construction of a jointed stand or joint support structure.
In its more particular aspects the jointed stand or the like of the present development is of the type comprising a pivot joint arrangement containing two joint or swivel heads, each having a coupling face or surface. The joint or swivel heads are arranged with the coupling surfaces facing each other. A common hinge pin passes through the joint or swivel heads. Tightening means act upon the hinge pin in order to press the joint or swivel heads against each other for locking the pivot joint arrangement. Two tube-like arms or arm members are interlinked by the pivot joint arrangement. Each arm has two oppositely located ends, one end facing the pivot joint arrangement and being anchored thereto and the other end carrying a hinge structure comprising a hinge element, a fixture for the hinge or joint element and a socket or seat for the hinge or joint element. Two thrust or push rods are provided, each of which extends through its related arm up to the associated joint or swivel head, and each such thrust or push rod can be displaced within the related arm thereof. The socket for the hinge element is mounted at the push rod. A transfer or transmission member is provided which possesses a first inclined surface or face. This transfer or transmission member is displaceable in the lengthwise direction of the common hinge pin by the tightening means and also in the direction of the related fixture and acts upon a neighboring end of the related push rod in order to displace the same in the direction of the fixture, so as to simultaneously lock the hinge or joint element with the pivot joint arrangement.
In a known jointed stand of this general type, as for example described in U.S. Pat. No. 3,910,538, granted Oct. 7, 1975, (see FIGS. 10 to 12 thereof), each of the push or thrust rods extending into the joint head is provided with a ring through which passes the hinge pin with clearance. A tightening nut is screwed on to one end of the hinge pin and the other end of such hinge pin is mounted to be longitudinally displaceable in the corresponding joint head. At the region of the last-mentioned joint head a conical transfer or transmission element is positioned upon the hinge pin. A further conical transmission or transfer element is displaceably mounted on the hinge pin at the region thereof which is positioned in the other joint head. The last mentioned transfer element is supported at the tightening nut by means of a thrust sleeve. The two transfer or transmssion members confront each other at their smaller diameters and only contact one point at the inner diameter of the rings mounted to the inner ends of the push rods by means of a generatrix of their conical surface. When the tightening nut is tightened the two transfer elements are positively moved towards each other. Consequently, the rings and in conjunction therewith the thrust or push rods are outwardly displaced and the two joint heads are pressed against each other by means of the rings. Thus, the pivot joint and simultaneously therewith the joints at the ends of the arms are locked. Also significant in this regard is U.S. Pat. No. 4,143,652, granted Mar. 13, 1979.
It is a disadvantage of this state-of-the-art arrangement that the hinge pin not only must take-up the axial force needed for pressing the two joint heads against each other, but also the shearing forces or loads originating from the co-action of the conical transfer elements with the rings at the push rods. Consequently, the hinge pin of the known jointed stand tends to cant, so that the conical transfer element which is displaceable upon the hinge pin may seize or bind thereon. Therefore, in such prior art jointed stand there are provided springs, each of which act upon the push rod and tend to move the same away from the associated fixture for the joint or hinge element located at the end of the respective arm. For locking the joints, this jointed stand also requires an additional force for overcoming the force of such spring.
According to a further prior art construction of jointed stand or joint support structure as known, for example, from U.S. Pat. No. 4,236,844, granted Dec. 2, 1980, (see FIGS. 2 to 9 thereof), each joint head is designed in a case-like manner and comprises a cup portion and a cover portion which can be displaced to a greater or lesser extent into the cup portion. Both the cup portions or members snugly engage each other at their base portions. The hinge pin is anchored to one of the cover portions and extends through both cup portions and the other cover portion and at that location carries an eccentrically arranged tightening lever by means of which the two cover portions may be displaced towards each other. Each cover portion has a wedge threadably connected thereto at the side thereof facing the internal space. The wedge or inclined face of the wedge member acts upon two rolls extending to both sides of the hinge pin and at right angles thereto. Both of the rolls act, on the other hand, upon another wedge member displaceable within the cup portion and formed in mirror-image relationship to the wedge member threadably connected to the cover portion, the inner end of the push rod engaging the displaceable wedge member. When the eccentric tightening lever is tightened, i.e. when the two cover portions are displaced towards each other, the threadably connected wedge member displaces the rolls in the direction of the other wedge member which then displaces the push rod towards the outside. At the same time the two rolls press the two cup portions at their bases against each other, so that the pivot joint is simultaneously locked along with the joints at the free ends of the arms.
In this prior art jointed stand construction the hinge pin practically only takes-up tension forces or loads, whereas the force originating from the push rods is supported in the cover portion of the corresponding joint head. On the other hand, each joint head comprises members (cup portion and cover portion) which are displaceable relative to each other and which design, in the case of contamination or soiling, may impair operability of the device. Additionally, upon tightening the eccentric tightening lever, the displaceable wedge member is also displaced transversely with respect to the push rod and this displacement is opposed by the friction prevailing between the cover portion and the displaceable wedge member bearing against the cover portion.